Effect of excess zinc on iron utilization by chicks fed a diet devoid of phytate and fiber

Two experiments were conducted to study the effects of excess dietary zinc (Zn) on iron (Fe) utilization by growing chicks fed a phytate and fiber-free casein-dextrose diet. Previous work in our laboratory had established 40 mg/kg Fe and 15 mg/kg Zn as minimum dietary requirements for young chicks. Three deficient levels of nonheme Fe (i.e., 5, 15, and 25 mg Fe/kg diet) were fed in the presence and absence of excess Zn from 8 to 22 days posthatching. At 10 times the Zn requirement, excess Zn had no effect on chick performance, blood hemoglobin (Hb) or hematocrit (Ht). At 100 times the Zn requirement, excess Zn depressed performance and decreased both Hb and Ht. Blood Hb responded linearly to Fe supplementation at 15, 150 and 1500 mg/kg dietary Zn. Slope of the Hb response curve (Hb regressed on Fe intake) was not affected by excess dietary Zn. It was thus concluded that excess dietary Zn has little or no effect on Fe utilization when a phytate and fiber-free diet is fed to chicks.